[Ifeffit] Phase corrected Fourier transforms

John J. Rehr jjr at leonardo.phys.washington.edu
Sat Sep 23 09:18:33 CDT 2006

Dear Juan Antonio,

  I personally feel that adding phase correction to the XAFS FT is
highly desirable, and I encouraged its implementation in Athena.
The reasons are the following:

1) Peaks in  non-phase corrected FT are substantially in error.
2) The non-linearity of the phase shifts in high-Z materials leads
to multiple-peaks, thus blurring the FT.
3) Theoretical phase shifts are good enough that adding phase correction
tends to correct the peak positions and the problems due to non-linearities.
4) Adding phase correction does no-harm to the fits. That is, one gets
the same results whether or not phase correction is included.
5) Adding phase correction gives a FT which can be more easily
interpreted "by eye", that is the peaks have a more physical interpretation.
On the contrary, non-phase corrected FTs can be mis-interpreted.

Overall, my view is that the phase correction is like a prescription
lens which gives a sharper image. While the image may not be perfect,
at least it's generally much superior to the non-phase corrected FT.

  J. Rehr

On Fri, 22 Sep 2006, Juan Antonio [iso-8859-1] Maciá Agulló wrote:

> Hi all,
> I have read Phase corrected Fourier transforms in Athena manual and now
> I have a big doubt, ¿phase correction or not in a publication?
> I have read also that this correction is different (more complete) in
> Artemis and I am not sure if I should correct also in Artemis and which
> path should I use and why.
> I saw many papers dealing with EXAFS fits and they showed a "calculated"
> bond distance, I think it is: d = Reff + deltaR, right?
> I also ask for a paper where I can find that deltaE is ok (even for
> high-Z backscatterers) if deltaE < 10eV.
> I have high correlations between ss and SO2, and deltaR and deltaE. I
> tried different fits but I can not eliminate them, then...is the fit
> wrong?
> Sorry for these easy questions but I am a novice in XAFS.
> Thank you very much.
> Best regards,
> JA

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